M. Glaser

Reverse annealing of the effective impurity concentration and long term operational scenario for silicon detectors in future collider experiments

Abstract Systematic investigations of the reverse annealing effect after radiation damage have been performed in particular for the change of the effective impurity concentration. The pronounced long term anneal observed at room temperature was further investigated by isochronal and isothermal studies. In order to demonstrate the radiation hardness of silicon detectors during 10 years of LHC operation an experiment was started at a higher temperature which compressed the real operational scenario to about 10 months.

Comparison of radiation damage in silicon induced by proton and neutron irradiation

The subject of radiation damage to Si detectors induced by 24-GeV/c protons and nuclear reactor neutrons has been studied. Detectors fabricated on single-crystal silicon enriched with various impurities have been tested. Significant differences in electrically active defects have been found between the various types of material. The results of the study suggest for the first time that the widely used nonionizing energy loss (NIEL) factors are insufficient for normalization of the electrically active damage in case of oxygen- and carbon-enriched silicon detectors. It has been found that a deliberate introduction of impurities into the semiconductor can affect the radiation hardness of silicon detectors.

Neutron-induced radiation damage in silicon detectors

Ion-implanted silicon pad detectors fabricated on different n-type and p-type silicon wafers with initial resistivities between 2.6 and 12.9 k Omega -cm have been irradiated with neutrons of approximately 1 MeV energy, up to a fluence of 5*10/sup 13/ n cm/sup -2/. The evolution of diode leakage current and capacitance characteristics is presented as a function of the neutron fluence. The reverse diode current increases proportionally to the neutron fluence. There is evidence that the doping of the initial n-type material evolves towards an intrinsic and inverts to an apparent p-type at fluences between 1*10/sup 13/ and 3*10/sup 13/ n cm/sup -2/, depending on the initial silicon resistivity. There is also evidence that p-type material remains of the same conduction type with a slight increase of the acceptor doping with fluence. The signal shape and the charge collection efficiency for incident beta particles have also been measured.<<ETX>>

First operation of a 72-k element hybrid silicon micropattern pixel detector array

Abstract We have constructed and tested silicon pixel detector arrays of 96 × 378 (36 288) sensor elements with 75 μm × 500 μm area. The low-noise signal processing circuit associated with each element occupies an identical area on a bump-bonded readout chip. The pixel cell response for ionizing particles is binary with an adjustable threshold between 4000 e − and 15 000 e − . Single chips, the array of 6 ladders and a double array have been characterized in particle test beams and in the Omega experiment WA97 at CERN. The two arrays together, staggered by ∼ 4 mm cover hermetically a 53 mm × 55 mm area with 72 576 pixels. The proportion of properly functioning pixels was 98% in the first 36 k pixel array and 80% in the second one. The ∼ 1% “always-on” pixels could be masked electronically. After masking the rate of “spurious noise hits” was −8 of the identified particle hits while with beam off no hits at all were recorded With a beam trigger most events consisted of a single cluster with a single hit. At the 8000 e − threshold an efficiency > 99% was measured. Tracks were reconstructed with a precision of 22 μm. The proportion of double hits (∼ 11%) depends only slightly on threshold and detector bias voltage, and for these double hits a precision of 10 μm on the particle position was obtained.

Study of characteristics of silicon detectors irradiated with 24 GeV/c protons between −20°C and +20°C

High resistivity ion-implanted silicon pad detectors have been irradiated at +20°C, +10°C, 0°C and −20°C with 24 GeV/c protons at a flux of ∼ 5 × 109cm−2s−1, up to fluences of ∼ 1.1 × 1014cm−2, and maintained at these temperatures during several months after the end of irradiation. The change of the diode reverse current, full depletion voltage and collection efficiency of the charge, deposited by relativistic electrons, are presented as a function of the proton fluence and of annealing time. It is found that operating the detectors below +10°C limits the diode reverse current and the bias voltage necessary to achieve full depletion. Moreover, at these temperatures, the charge collection efficiency for an integration time of 20 ns (typical of LHC operation) is better than 90% for 300 μm detectors irradiated to a fluence of 1014 cm−2 and biased at 160 V.

Dosimetry Assessments in the Irradiation Facilities at the CERN-PS Accelerator

At the CERN Proton Synchrotron (PS) accelerator complex, two experimental zones allow the irradiation of samples in a 23 GeV pure proton beam and in a secondary particle environment dominated by 1-MeV neutrons and gamma rays. In this paper, a review of the operative irradiation systems named IRRAD1 and IRRAD2 is presented, as well as the improvements in the techniques used for the beam characterizations and dosimetry

Conception of an integrated sensor for the radiation monitoring of the CMS experiment at the large hadron collider

The concept of an active integrated dosimetric sensor for the radiation monitoring of the Compact Muon Solenoid experiment at the CERN (European Center for Nuclear Research) Large Hadron Collider is presented. The sensor, based on RadFET, OSL, p-i-n diode, and pad detector dosimeters, will measure both ionizing and nonionizing energy losses in the harsh radiation environment produced by hadron interactions.

Studies of radiation hardness of oxygen enriched silicon detectors

Abstract Detectors for high-energy particles sustain a substantial amount of structural defects induced by the particles during the operation period. Some of the defects have been found to be electrically active, degrading the detectors performance. Understanding the mechanisms of the electrical activities and learning to suppress their influence are essential if long “lifetime” detectors are required. This work reports about radiation hardness of silicon P-I-N devices fabricated from oxygen enriched high resistivity material. The high and nearly uniform concentration of oxygen in Float Zone silicon has been achieved by diffusion of oxygen from SiO 2 layers.

Radiation Monitoring in Mixed Environments at CERN: From the IRRAD6 Facility to the LHC Experiments

RadFET and p-i-n diode semiconductor dosimeters from different manufacturers will be used for radiation monitoring at the Experiments of the CERN LHC accelerator. In this work these sensors were exposed over three months in the CERN-IRRAD6 facility that provides mixed high-energy particles at low rates. The aim was to validate the operation of such sensors in a radiation field where the conditions are close to the ones expected inside full working LHC particle detectors. The results of this long-term irradiation campaign are presented, discussed and compared with measurements by other dosimetric means as well as Monte Carlo simulations. Finally, the integration of several dosimetric devices in one sensor carrier is also presented.

Performance of bulk SiC radiation detectors

SiC is a wide-gap material with excellent electrical and physical properties that may make it an important material for some future electronic devices. The most important possible applications of SiC are in hostile environments, such as in car/jet engines, within nuclear reactors, or in outer space. Another area where the material properties, most notably radiation hardness, would be valuable is in the inner tracking detectors of particle physics experiments. Here, we describe the performance of SiC diodes irradiated in the 24 GeV proton beam at CERN. Schottky measurements have been used to probe the irradiated material for changes in I–V characteristics. Other methods, borrowed from III–V research, used to study the irradiated surface include atomic force microscope scans and Raman spectroscopy. These have been used to observe the damage to the materials surface and internal lattice structure. We have also characterised the detection capabilities of bulk semi-insulating SiC for α radiation. By measuring the charge collection efficiency (CCE) for variations in bias voltage, CCE values up to 100% have been measured.